Electric pressure-control snap switch



April 1, 1969 E. M. EGLI ELECTRIC PRESSURE-CONTROL SNAP SWITCH orz SheetFiled Feb.

M FIGS I Ernsf M. E

911' INVENTOR.

Attorney April 1, 1969v E. M. EGLI ELECTRIC PRESSURE-CONTROL SNAP SWITCHFiled Feb. 2, 1967 Sheet NN 10.5 523 x/ Ernst M. Egli INVENTOR 3 m3 mokTy maGMOL q 325% kuEzou N 10.8 mumma v Attorney United States Patent3,436,502 ELECTRIC PRESSURE-CONTROL SNAP SWITCH Ernst M. Egli, Zurich,Switzerland, assignor to Patinvest Patentund Investment A.G., Chur,Switzerland Filed Feb. 2, 1967, Ser. No. 613,499

Claims priority, application Germany, Feb. 8, 1966 and Feb. 15, 1966, P38,726, Patent 1,939,186 Int. Cl. Htllh 35/40 US. Cl. 200-83 ClaimsABSTRACT OF THE DISCLOSURE Background of the invention The presentinvention relates to an electric snap-action switch for controlling thepressure of liquids or gases and especially suitable for being employedfor a clothes washing or dish-washing machine or the like, wherein thisswitch is provided with at least one contact spring which projectsbetween a pair of fixed switch contacts and the operation of which maybe controlled by the movements of an element, for example, a diaphragm,which is subjected to the pressure of a liquid or gas and then acts uponan intermediate control lever which is connected to the contact springby a snap spring and is also acted upon by an adjusting spring in adirection substantially opposite to the direction of movement of theelement when subjected to an increasing pressure of the liquid or gas.

In a snap-action switch of this type, the position of the oppositechange-over points or contacts of the switch, hereafter called thechange and re-change points, are determined by the force of theadjusting spring acting upon the control lever in the direction oppositeto the action of an element, for example, a diaphragm, which isconnected to the control lever and is subjected to and movable under thechanging pressure of a liquid or gas. The distance between these changeand re-change points is, however, dependent upon the distance betweenthe fixed switch contacts and also upon the elasticity constant of theadjusting spring. The minimum distance between these contacts is, inturn, dependent upon the admissible flashover or breakdown voltage ofthe switch, while the maximum distance is dependent upon the geometricproperties of the switch and its housing. The dimensions of the switchhousing, however, also determine the dimensions of the adjusting springwhich, in turn, affect the elasticity constant and the adjustability ofthis spring. If, therefore, the contact spring should change over fromone fixed contact to the other only when a relatively strong force isexerted upon the control lever by the element, for example, a diaphragm,which is acted upon by the pressure to be controlled e.g. by arelatively high liquid or gas pressure the necessary spring force of theadjusting spring can only be attained if this spring has such a highelasticity constant that it will produce an opposing or bracing force ofsufficient strength. This, however, means that the minimum distancebetween the change and rechange points must also be relatively large.Prior to this invention, attempts were made to overcome this difficultyby installing in each snap-action switch an adjusting spring of astrength in accordance with the particular pressure to be controlled.However, since a control of high pressures also requires adjustingsprings with higher elasticity constants, these known switches still hadthe disadvantage that the minimum distance between the change andre-change points of the contact spring also had to be relatively large.

Summary of the invention It is an object of the present invention toprovide a spring system for a snap-action switch of the characterdescribed, such that the minimum distance between the change andre-change points may be made as small as possible, while the maximumdistance between the change and re-change points may be sufiicientlylarge.

According to the invention, this object is attained by providing thesnap-action switch with an additional compensating spring, a forcecomponent of which also acts upon the control lever but in a directiondifferent from the action of the adjusting spring and exerts a torqueupon the control lever which extends in the opposite direction to thetorque which is exerted upon this lever by the adjusting spring.

By the provision of this compensating spring a torque is produced andexerted upon the control lever which is superimposed on the torque whichis produced by the adjusting spring. Due to the pivoting movement of thecontrol lever, this additional torque at first increases in strengthand, after the control lever is pivoted for a certain distance, itsstrength again decreases. The increase of this torque is caused by theincrease in the length of the lever moment arm which is determined bythe distance between the line connecting the bearing points of thecompensating spring and the pivotal axis of the control lever, whereasthe decrease of this torque is caused by the release of the compensatingspring.

The superimposition of the two opposing torques, one of which isproduced by the adjusting spring and the other by the compensatingspring, has the eflect that the resultant torque line at first ascendsvery steeply substantially in the direction of travel of the controllever and then slopes off to some extent after the control lever reachesa central area between the minimum change point and the maximum changepoint. This, however, means that within the area adjacent to there-change point and also to the minimum change point only a smallresultant torque will be required for producing a movement of thecontrol lever. Within the area adjacent to the maximum change point,however, a greater torque will be required for producing the samemovement of the control lever. This operation, which prior to thisinvention could only be attained by employing different snap switches orby exchanging the adjusting springs for others of a different strength,may now be attained in the same snap switch by one and the same springsystem, and it only requires the initial tension of the same adjustingspring to be varied when the switch is to be used for controllingdifferent pressures. It is, however, important that, regardless of theinitial tension to which the adjusting spring might be adjusted, theswitch will be designed so as to permit the lowest change point and there-change point to be spaced at a short distance from each other andalso to insure that the lowest change point and the highest change pointwill be separated by a sufficiently large distance.

The compensating spring according to the invention is preferablyprovided in the form of an omega ((2) leaf spring, one end of which issupported on a fixed or adjustable point of the switch, while its otherend acts upon the control lever. In place of an omega leaf spring it ishowever, also possible to employ a curved leaf spring of another shapeor a coil compression spring or the like. Another possibility ofinfluencing the characteristic of the torques consists, according to theinvention in providing a compensating spring which has a linear orprogressive characteristic but preferably a negative or digressivecharacteristic.

If a snap-action switch of the above-mentioned type is designed as apolyphase switch and provided with sever-a1 identical switch systems,and if the diaphragm therefore acts upon several control levers, theadditional difliculty occurs that, when one of the control levers yieldsunder the pressure which acts upon the diaphragm, the diaphragm willtilt at an angle. This tilting of the diaphragm has the disadvantagethat the tappets, which are secured to the diaphragm plate and act uponthe control levers by means of a shoulder on each tappet from which ashort pin projects through a bore in the respective control lever, willalso tilt so that the projecting pins will engage the walls of the boresand thereby cause frictional losses which may result in an inaccurateoperation of the switch.

These difliculties, which existed in previous snap-action switches, maybe overcome, according to the invention, by making the supporting plateof the flexible diaphragm of a flexible material so that this supportingplate may likewise bend and therefore permit the tappets which aresecured to the diaphragm supporting plate to yield laterally so that thefrictional contact which previously occurred between the tappets and thecontrol levers will be avoided.

If the switch is provided with several similar switch systems which arecontrolled by a common diaphragm and each of which consists of a pair offixed contacts, a contact spring, a control lever, a snap spring, andadjusting spring, and a compensating spring, the further great advantageis attained that the switch may be easily assembled and, if desired ornecessary, its individual elements may also be easily exchanged forothers of the same kind.

Another advantageous feature of the invention resides in providing theouter edge portion of one of the two parts of the switch housing with aninwardly projecting bead which, when the housing is being closed, slideselastically over and behind, the outwardly projecting edge of the otherhousing part so as to grip the latter securely. Because of thisconstruction it is only necessary after the switch elements have beeninstalled in the housing to press the two parts of the housingtelescopically into each other so that the bead on the elastic edgeportion of the one housing part will snap over the outwardly projectingedge portion of the other housing part and thereby grip the lattersecurely and seal the housing tightly.

The features and advantages of the present invention will become moreclearly apparent from the following detailed description thereof whichis to be read with reference to the accompanying drawing, in whichFIGURE 1 shows a cross section of a single-pole switch according to theinvention;

FIGURE 2 shows a cross section of a polyphase switch according to theinvention;

FIGURE 3 is a diagrammatic illustration of the torques acting upon thecontrol lever; and

FIGURE 4 is a torque diagram showing the relation of the torques to thecourse of movement of the control lever.

The single-pole pressure-control switch according to the invention asillustrated in FIGURE 1 comprises a diaphragm 1 which is mountedperipherally within a housing 7 and may be acted upon by the pressure ofa liquid or gas entering the lower part of the switch housing through aninlet fitting 2. Diaphragm 1 carries a supporting plate 3 to which acentral tappet 4 is secured; the tappet 4, in turn, acts upon a controllever 5 which is mounted at one end on housing 7 so as to be pivotableabout this end in a vertical direction. At the point of connection oftappet 4 with control lever 5, the other side of this lever is actedupon by the lower end of an adjusting spring 6, the upper end of whichis located within a cap 8 which 4 is screwed into the switch housing 7so as to be adjustable to different levels to vary the strength ofspring 6.

The control lever 5 is further associated with a contact spring 9 whichis likewise secured at one end to housing 7 and provided with alongitudinal slot through which the control lever 5 may pivot from oneside of contact spring 9 to the other. The free other end of contactspring carries a contact 10 which is located between the two fixedswitch contacts 11 and 12 with which it is alternately adapted toengage. At a certain distance from its free end, contact spring 9 ispivotably connected to one end of a snap spring 13 in the form of abarrel spring, the other end of which is likewise pivotably connected tothe free end 14 of control lever 5 in such a manner that, as soon as thecontrol lever is pivoted and passes the plane of contact spring 9, itsnaps over to the other side, thereby pivoting the contact spring 9 inthe opposite direction and thus reversing the switching position or modeof contact 10 relative to the fixed contacts '11 and 12.

The free end 14 of control lever 5 is further provided with adownwardly-bent extension 15 which serves as an abutment for one end ofa compensating spring 16 in the form of an omega leaf spring, the otherend of which is supported on a fixed or vertically adjustable abutrnent17.

The stroke of control lever 5 in the upward direction is limited by astop projection 18 on the upper wall of housing 7, while the downwardstroke of control lever 5 is limited by the lowest position of thetappet 4, that is, the position in which at a decrease of pressure onthe diaphragm 1, this diaphragm rests upon the upper edge of the annularflange 19 on the bottom wall of housing 7 around the opening of theinlet 2..

FIGURE 2 illustrates a polyphase pressure-control switch according tothe invention, in which the components which are similar to those inFIGURE 1 are designated by the same reference numerals. The three springsystems each of which also consists in this case of a control lever 20,a contact spring 9, a snap spring 13, and a compensating spring 16 aredisposed laterally adjacent but in reverse positions to each other.

This embodiment of the invention differs further from that as previouslydescribed by the fact that the control lever which in this case isdesignated by the numeral 20 is bent downwardly from its fixed end sothat its pivoting range lies outside of the pivoting range of contactspring 9. Contact spring 9 therefore no longer needs to be slotted topermit the control lever 20 to pivot through the contact spring.Similarly as in the first embodiment, the pivoting range of controllever 20 is limited by two stop members which in this case aredesignated by the numerals 21 and 22.

FIGURE 3 is a diagrammatic illustration of the forces WhlCh act upon thecontrol lever or levers 5 or 20. First, the adjusting spring 6 exerts apressure in the direction of the arrow J upon the control lever 5 or 20which results in a positive torque M a-J in a counterclockwise d rectionof the lever arm a which is determined by the distance between the pivotpoint of control lever 5 or 20 and the direction of pressure I of theadjusting spring 6 upon the control lever. Furthermore, the free end ofcontrol lever 5 or 20 is acted upon in the direction of the arrow S bythe pressure of snap spring 13 which due to the lever arm b likewiseresults in a positive torque M =b-S in a counterclockwise direction.This lever arm b is determined by the distance between the direction ofthe force S from the pivot point of control lever 5 or 20. Finally,control lever 5 or 20 is acted upon the compensating spring '16 which isbraced on the points 14 and 17 and exerts a pressure in the direction ofthe arrow K which is determined by the line of connection between thepoints 14 and 17 and is spaced from the pivot point of control lever 5or 20 by a lever arm 0. Due to the force K which is produced by thecompensating spring 16, a negative torque M =c-K (in the clockwisedirection) results; this torque is opposed to the torque which isproduced and the joint action of the adjusting spring 6 and the snapspring 13.

These particular relations of the different torques acting upon thecontrol lever 5 or 20 are indicated in greater detail in the diagram asshown in FIGURE 4, in which the course of these torques is plotted inrelation to the course of travel of control lever 5 or 20 which islimited by the lower stop member 22 and the upper stop member 21. FIGURE4 further shows, at a certain distance from the line indicating thelower stop 22, the line 23 which indicates the re-change point and mustbe located at a higher level than the lower stop line 22 because apositive torque must still be prevalent at the re-change point 23 inorder to insure a proper engagement between the adjusting spring 6 andcontrol lever 5 or 20. Above and parallel to this re-change point line23, extends the line 24 which designates the lowest change point and isspaced from the lower stop line 22 at a distance A which again dependsupon the distance between the switch contacts 11 and 12. Finally, thehighest change point is indicated by the line 25 which, of course, liesbelow the line which represents the upper stop 21. The distance Bbetween the two lines 24 and 25 indicates the range within which thedesired change point may be located.

The diagram in FIGURE 4 further shows two straight inclined dotted linesMJ and M which represent the path of the torque M a-l which is producedby the adjusting spring *6. These two straight lines M and M differ fromeach other by the fact that according to line M the adjusting spring 6is given a higher initial tension and that this line is thereforeshifted more to the right.

The left part of the diagram according to FIGURE 4 further indicates bya dot-and-dash line the torque curve M which results from the product ofthe force K of the compensating spring 16 multiplied by the lever arm asindicated in FIGURE 3. This torque M has a negative value, and the forceK of compensating spring 16 and thus also accordingly the torque M areof such a magnitude that the latter will be negative along the entireextent of travel of control lever or 20 and that the torque line willnot intersect the vertical zero line except at points above and belowthe two stop lines 21 and 22, respectively. As the movement of thecontrol lever 5 or 20 progresses, the value of the torque M will atfirst increase since by the action of the upwardly moving diaphragm thecontrol lever 5 or 20 will be pivoted in the clockwise direction whichwill result in a progressive increase of the length of the lever arm cand thus also in a corresponding increase of the torque M When thecontrol lever 5 or 20 has passed approximately one half of its entiredistance of travel, the compensating spring 16 will be released and thespring force K will therefore be reduced to such an extent that even thefurther increase in the length of the lever arm c can no longercompensate this reduction of the spring force K.

As previously mentioned, the three torques M M and M are superimposed oneach other. Since the torque M which is produced by snap spring 13 isrelatively small, it will be neglected in the following observations.When the torque M is then superimposed on the two torques M and M thetwo torque lines (M +M and (M +M will result which are shown by solidlines in FIGURE 4. These two equal torque lines (M +M and (M -i-M atfirst ascend very steeply and their slope then decreases approximatelywithin their central part. This curving of the torque lines (M -I-M and(M +M is caused entirely by the course of the torque line M Acomparison, for example, of the course of the torque line (M +M with thecourse of the torque line M shows that, if the control lever 5 or 20should travel the distance A, a considerably smaller torque will berequired than when merely the adjusting spring 6 were present whichproduces the torque M Since a linear relation exists between thesetorques and the opposing force which is exerted by the diaphragm l1, andthus also between these torques and the pressure which is exerted uponthe diaphragm, it is manifest that the lowest change point 24 may beplaced at a very small distance from the re-change point 23. Forpivoting the control lever 5 or 20 to the highest change point 25, itis, however, necessary to provide considerably larger torques.

If the change points 23, 24, and 25 are to be shifted upwardly, it isnecessary to give the adjusting spring 6 an initial tension so that theline M and thus also the line (M +M will be shifted farther toward theright. The distances A and B between the re-change point 23 and thelowest change point 24 and between the lowest change point 24 and thehighest change point 25 remain, how-ever, the same which may also beseen from the following numerical example:

If the re-change point 23 is located within the torque line (M -I-M forexample, at a pressure of 20 mm. W.G., the lowest change point 24 mayalready occur at a pressure of 50 mm. W.G. so that the difference onlyamounts to 30 mm. W.G. The highest change point 25, however, occurs inthis case at a pressure of mm. W.G. If the adjusting spring 6 is thenadjusted to have a higher tension, greater switching forces will berequired which, in turn, require higher pressures which would then haveto amount to, for example, mm. W.G., mm. W.G., and 200 mm. W.G. It isthen, however, essential that at such high change points the pressuredifferences A and B, and especially the small pressure differences Abetween the re-change point 23 and the lower change point 24 will remainunchanged. When employing only one adjusting spring 6 and onecompensating spring 16, it is therefore possible to attain low as wellas high change points, even though the small pressure differences Abetween the re-change point 23 and the lowest change point 24 remainunchanged.

If the slope of the upper range of the torque line (M -i-M should bestill less inclined, this may be attained by employing a compensatingspring 16 with a digressive characteristic.

As further illustrated in FIGURES l and 2, the diaphragm 1 is providedwith a thicker outer ring 26 which is clamped between the two oppositeannular surfaces 27 and 28 of the upper housing part 7 and the lowerhousing part 29. This lower housing part 29 which is preferably made ofplastic has an outer rim 30 which encloses and projects upwardly fromthe outer ring 26 of diaphragm 1 and is slightly elastic. On its upperedge, it has an inwardly projecting bead 31 which, when the two-partswitch housing is closed, snaps over the outer edge 32 of the upperhousing part 7 and thus connects the two housing parts 7 and 29 tightlyto each other. In order to permit the upper housing part 7 to be easilypressed into the lower housing part 29 when the switch is beinginstalled, the inner edge 33 of bead 31 is inwardly inclined in themanner as shown in FIGURES 1 and 2.

For properly supporting the diaphragm 1 especially in the polyphaseswitch according to FIGURE 2, the tappets 4 on the diaphragm plate 3project loosely through bores 34 which are provided in the controllevers 20. A three-point support of the control levers 20 on thediaphragm plate 3 is attained by providing not only a second, onlypartly indicated switch system behind the system which is completelyshown in FIGURE 2 but also a third switch system which is located infront of the plane of the drawing. Since each of the adjusting springs 6of the three switch systems is supported at its upper end within a cap 8which is screwed into the upper housing part 7 so as to permit it to beadjusted to different levels, it is possible to adjust the threeadjusting springs 6 to different initial tensions which, in turn meansthat the forces which are exerted by the adjusting springs 6 so as tobrace the diaphragm 1 will be of different strengths and that, as soonas a pressure is exerted upon the diaphragm 1, this pressure willovercome the force of that adjusting spring 6 which has the lowestinitial tension. This, in turn, means that the diaphragm 1 will bepartly lifted and bent, provided the diaphragm-supporting plate 3 ismade according to the invention of an elastic material and is thereforecapable of yielding when so moved. This, however, insures that thetappets 4 which project through the bores 33 in the control levers 20will not jam therein and that therefore also no undue friction willoccur between the tappets and the walls of bores 33.

Although my invention has been illustrated and described with referenceto the preferred embodiments thereof, I wish to have it understood thatit is in no way limited to the details of such embodiments but iscapable of numerous modifications within the scope of the appendedclaims.

Having thus fully disclosed my invention, what I claim is:

1. An electric snap-action switch for controlling the pressure ofliquids or gases, comprising a housing, a diaphragm peripherally andtightly secured to the outer wall of said housing and dividing the sameinto afirst part and a second part, said first housing part having aninlet opening through which the pressure to be controlled may enter saidfirst housing part and act upon one side of said diaphragm so as toshift said diaphragm in the direction of said second housing part, atleast one pair of fixed contacts mounted in said second part and spacedfrom each other, at least one contact spring having a fixed end mountedon said housing within said second part and a free end projectingbetween said fixed contacts and adapted to engage with one of saidcontacts when said pressure is below a certain value and With the othercontact when said pressure increases above said value, at least onecontrol lever having one end connected to said housing adjacent to thefixed end of said contact spring and pivotable at said fixed endrelative to said contact spring, at least one tappet having one endsecured to said diaphragm and another end engaging one side of saidcontrol lever, at least one adjusting spring having one end secured tosaid housing and another end engaging the other side of said controllever so as to exert a torque thereon, means for varying the strength ofsaid adjusting spring in a predetermined relation to the pressure to becontrolled, a snap spring having an axis normally extending to saidcontrol lever and said contact spring and interconnecting said controllever and said contact spring, said snap spring being adapted when saidpressure increases beyond said value and said lever is pivoted in afirst direction together with said lever and thereby to pivot saidcontact spring quickly in the opposite second direction and fromengagement with the first into engagement with the second fixed contact,said snap spring being further adapted when said pressure decreasesbelow said value to snap over in said second direction together withsaid lever and thereby to pivot said contact spring in said firstdirection and from engagement with said second into engagement with saidfirst contact,

and a compensating spring having a force component acting upon saidlever in a direction different from the action of said adjusting springand exerting a torque upon said lever extending in the oppositedirection to said torque exerted thereon by said adjusting spring.

2. A switch as defined in claim 1, wherein said compensating spring is acurved leaf spring one end of which is supported on a fixed part of saidswitch, while the other end of said curved leaf spring acts upon saidcontrol lever.

3. A switch as defined in claim 1, wherein said compensating spring hasa degressive characteristic.

4. A switch as defined in claim 1, further comprising fixed stop membersfor limiting the pivoting range of said control lever.

5. A switch as defined in laim 1, wherein said contact spring isprovided with a longitudinal slot and said control lever is pivotablethrough said slot from one side of said contact spring to the other.

6. Aswitch as define-d in claim 1, wherein said control lever is bent insuch a manner that its pivoting range is located outside of the pivotingrange of said contact spring.

7. A switch as defined in claim 1 and forming a polyphase switchassembly having a plurality of switch systems all of which are actedupon by said one diaphragm and each comprising a pair of said fixedcontacts, said contact spring, said control lever, said snap spring,said adjusting spring and said compensating spring.

8. A switch as defined in claim 7, wherein said switch systems aredisposed laterally adjacent but in reverse positions to each other.

9. A switch as defined in claim 7, further comprising a flexible plateon said diaphragm for supporting the same, said tappets for acting uponsaid control levers of said switch systems being secured to saidsupporting plate. 10. A switch as defined in claim 1, wherein saidhousing consists of separate upper and lower parts, one of said housingparts having an outer edge portion with a bead thereon projecting in onedirection, and the other housing part having an outer edge portionprojecting in the opposite direction, said bead being adapted to snapelastically over the outer edge portion of said other housing part whensaid two housing parts are telescopically connected to each other.

References Cited UNITED STATES PATENTS 2,636,093 4/1953 Clark et al.2,813,944 11/1957 Tyzack 2,934,618 4/1960 Beller et al.

ROBERT K. SCHAEFER, Primary Examiner.

H. BURKS, Assistant Examiner.

US. Cl. X.R.

